Polymerization of cyclic carbamates



United rates 2,806,017 POLYMERIZATION OF CYCLIC CARBAMA'I'ES Erhart K.Drechsel, Springdale, Conn., assignor to American Cyanamid Company, NewYork, N. Y., a corporation of Maine No Drawing. Original applicationAugust 9, 1952, Serial No. 303,609, now Patent No. 2,744,897, dated May8, 1956. Divided and this application November 29, 1955, Serial No.549,889

5 Claims. (Cl. 260-775) where n represents a whole number selected fromthe class consisting of 3 and 4. The cyclic carbamates embraced by thisformula are 2-ketotetrahydro1,3-oxazine, which also may be namedO,N-trimethylene carbamate, and 2 ketohexahydro 1,3 oxazepine, whichalso may be named O,N tetramethylene carbamate. They have many valuableuses in industry, for example as plasticizers of resinous and othermaterials, and as intermediates in the production of other valuablecompositions. They constitute a particularly useful class of monomersfrom which polymeric products are produced by isomerization. The solid,higher-molecular-weight polymers (e. g., those having an averagemolecular weight not less than 10,000, more particularly an averagemolecular weight ranging from 10,000 or 20,000 to 75,000 or 100,000 orhigher, as determined from viscosity measurements of dilute solutionsusing thte Staudinger equation) are fiber-forming polymers from whichfibers or filaments having particular and peculiar properties can beproduced. The solid polymers of the cyclic carbamates embraced byFormula I are useful in coating, molding, laminating adhesive,textile-treating, paper-treating and other applications where othersynthetic resins are now being used.

Various methods can be employed for producing the cyclic carbamatesembraced by Formula I. One convenient and economical method comprsisesefiecting a Beckrnann rearrangement of the corresponding hydroximic acidrepresented by the general formula II HO-N It O(CE[;) where n has thesame meaning as given above with reference to Formula I, and thenisolating a cyclic carbamate corresponding to the hydroximic acidemployed from the resulting reaction mass, e. g., by distillation underheat and vacuum.

The Beckmann rearrangement as applied to other compounds is vvell knownin chemistry (see, for instance, Sidgwicks The Organic Chemistry ofNitrogen, new edition, revised and rewritten by Taylor and Baker, 1937,especially pages 19, 49, 177, 199-201, 472 and 573; also, U. S. Patents2,249,177 and 2,234,566). The equation 2,806,017 Patented Sept. 10, 1957acid O N In Equations III and IV, n has the same meaning as given abovewith reference to Formulas I and II.

Another suitable method for preparing one of the cyclic carbamatesembraced by Formula I, specifically 2-ketotetrahydro 1,3 oxazine,comprises efiecting alcoholysis of N (3 hydroxypropyl) O alkyl carbamateunder heat, and isolating 2 ketotetrahydro 1,3 oxazine from theresulting reaction mass. The O-alkyl substituent is preferably anO-(lower alkyl) substituent, e. g., O-methyl, -ethyl, -propyl,-isopropyl, -n-butyl, -isobutyl, -sec.- butyl, -amyl, etc; Thus, I mayprepare Z-ketotetrahydro 1,3 oxazine by efiecting reaction betweenequimolecular proportions or with the one reactant from,

for example, 0.01 to 10 mole percent in excess of the other) ofB-aminopropanol and a dialkyl carbonate, e. g., diethyl carbonate,dipropyl carbonate, etc., to obtain the corresponding N (3hydroxypropyl) O alkyl carbamate, distilling oh the alcohol by-productof the initial reaction, and continuing the distillation under heat(usually also under vacuum) to remove the remaining combined alcohol,whereby the N (3 hydroxypropyl) 0- alkyl carbamate is cyclized and2-ketotetrahydro-L3-oxazine is formed, after which the said 1,3-oxazineis isolated, e. g., by distillation, from the reaction mass. Thetemperature required for removing the remaining combined alcohol andforming the 1,3-oxazine varies depending, for example, upon theparticular alcohol to be removed and the vacuum (if any) employed, e.g., from 40 C. to 200 C.

The conversion of the N-(B-hydroxypropyl)-O-alkyl carbamate to thecyclic carbamate, whereby combined alcohol is evolved, is preferablycarried out with the aid of an alcoholysis catalyst. Examples of suchcatalysts which may be used are alkali metals, alkaline-earth metals andcertain heavy metals (e. g., lead, zinc, manganese, etc.) or oxides,carbonates or salts thereof. Any suitable amount of an alcoholysiscatalyst can be employed, as desired or as conditions may require, e.g., from 0.0001% to 1 or 2% by weight of the intermediate, N- 3-hydroxypropyl) -O-alkyl carbamate.

During the preparation of the cyclic carbamate and its isolation bydistillation, some polymer of the carbamate also is formed in varyingamounts and remains in the residue. 7

The polymer of the carbamate also can be produced by isomerization ofthe isolated monomer, e. g., by heating the said monomer at temperaturesranging from about 40 to 200 C. The isomerization can be accelerated bythe use of a suitable catalyst or catalysts, for instance, traces of amonohydric alcohol (e. g., methyl, ethyl, propyl, etc., alcohols), or ofan alkali-metal carbonate, e. g., potassium carbonate, etc., or of aFriedel-Crafts tion.

. 3 7 catalyst, e. g., zinc chloride, .aluminum chloride, sulfuric acid,hydrogen fluoride, boron trifluoride, BFs-ethyl ether complex, etc.Traces of Water also may sometimes be used advantageously as: apolymerization .catalyst. With certain catalysts, for exampleFriedekCraIts catalysts,

the isomerization of the monomer to a polymer may be- Example 1 To areaction vessel is added 118 parts of diethyl carbonate at 25 C., afterwhich 75 parts of 3-aminopropanol is added with stirring. This is in theratio of 1 mole of diethyl carbonate to 1 mole of 3-aminopropanel.Initially a two-phase system forms in the reaction vessel; however, whenthe reaction mass is stirred for about 16 hours at room temperature (2530 (3.), it becomes clear and homogeneous.

The reaction vessel is now fitted with a column and a distillation head.An alcoholysis catalyst, e. g., a few shavings of metallic sodium (about0.5 part), are added to the reaction mass comprising the intermediatereaction product, HO (CH2)3NH.COOC2H5, and the ethanol by-product of theinitial reaction is removed by distilla- Some of the combined ethanol isremoved'at the same time. In this distillation 72 parts of volatilematter comprising mostly ethanol and boiling at 78 80 C. is recovered.After changing the apparatus for vacuum distillation, an additional 18parts of volatile matter (also comprising chiefly ethanol) is removedunder vacuum. About 10% of this material is apparently not ethanol. Thetotal conversion is then calculated as follows:

Vacuum distillation is continued with the pressure lowered to 1.5 to 2mm. mercury while gradually raising the temperature. At a vaportemperature of l50155 C. a yellow, viscous oil comprising2-ketotetrahydro-1,3- oxazine is distilled ofi. This oil is collected ina receiver surrounded by Dry Ice and wherein it solidifies. Aftercollecting 35 parts of this material, the vapor temperature in thedistilling head drops sharply and no more distillate is recovered.

The residue in the reaction vessel is a dark brown resin (polymer ofZ-ketotetrahydro-1,3-oxazine), which, even when hot, can be poured onlywith dificulty. It has an average molecular weight substantially above10,000 as calculated from viscosity measurements of a dilute solutionusing the Staudinger equation. It is a fiber-forming material. Fibers orfilaments can be formed from this polymer by conventional melt-extrusiontechnique or by other means. The extruded filaments can be drawn eitherhotor cold. The drawn 'orstretched fibers or filaments show, bycharacteristic X-ray patterns, orientation along the fiber axis.

The monomeric reaction product comprising 2-ketotetrahydro-l,3-oxazineis a liquid at room temperature (2530 ,C.). It is readily soluble inwater, methanol and benzene but is insoluble in hexane. Attempts torecrystallize it from solvent and non-solvent mixtures,

e. g., mixtures of hexane and benzene, and of hexane and methanol,result in oiling out of the liquid product. From the setting-point curvea melting-point value of 212 C.21.4 C. is obtained.

4 The above reaction may be illustrated by the. following equation:

z-ketotetrahydro-L3-oxazine Polymer (isomerization product) of2-ketotetv rahydro-1,3-oxazine In the above equation it represents thenumber of the recurring units in the polymer molecule, e. g., from 2Example 2 To 12 parts of sulfuric acid is added 10 parts oftetramethylene hydroximic acid. This mixture is heated cautiously untilbubbles first appear. The heating is discontinued and the violentreaction which ensues permitted to subside. This acid solution is cooledto 0 C. and carefully made alkaline with 24% potassium hydroxidesolution, taking care to keep the temperature below 10 C. with adequatecooling at all times. The potassium sulfate which separates is washedtwice with 5 parts of chloroform. The neutral filtrate is extracted fivetimes with 10 parts of chloroform. The combined chloroform extracts arewashed with 5 parts water to eliminate traces of alkali. Removal of thechloroform solvent yields the desired 2-ketohexahydro-1,3-oxazepine.

Similar technique can be used in making d ro-1,3-oxazine fromtrimethylene hydroximic acid.

Example 3 To parts of the isolated Z-ketotetrahydro-1,3-oxazine ofExample 1 is added 1 part of potassium carbonate. The resulting mixtureis heated for 2 hours while passing a slow stream of pre-purifiednitrogen gas over the mass. During this heating period the liquidmonomer U. S. Patent No. 2,701,246, dated February 1, 1955, claims aremade to the method of preparing 2-ketotetra-' hydro-1,3-oxazine whichcomprises effecting alcoholysis of N-(3-hydroxypropyl)-O-lower alkylcarbamate at a- C., and isolating 2- ketotetrahydro-1,3-oxazine from theresulting reaction temperature of from 40 C. to 200 mass.

I claim: 1. The method of preparing a new polymeric material2-ketotetrahy which comprises heating a cyclic carbamate represented bythe general formula Where n represents a whole number selected from theclass consisting of 3 and 4 at a temperature of from about 40 C. toabout 200 0, thereby to convert the said carbamate to a linear polymer.

2. A method as in claim 1 wherein the cyclic carbamate is heated Whileadmixed with a monohydric alcohol as a catalyst for the reaction.

3. A method as in claim 1 wherein the cyclic carbamate is heated whileadmixed with an alkali-metal carbonate as a catalyst for the reaction.

4. The method of preparing a new polymeric material which comprisesheating 2-ketotetrahydro-1,3-0Xazine at a temperature ranging from about40 C. to about 200 C. until the said oxazine has been converted to alinear polymer.

5. The method of obtaining a new polymeric material which comprisesconverting N-(3-hydroxypropyl) -O- alkyl carbamate at a temperature offrom about 40 C. to about 200 C. to Z-ketotetrahydro-l,3-oxazine,distilling Z-ketotetrahydro-1,3-oxazine from the reaction mass, andcollecting the linear polymer of 2-ketotetrahydro-1,3- oxazine thatremains in the residue and which is produced during the aforesaidpreparation and isolation of the said oxazine.

References Cited in the file of this patent UNITED STATES PATENTS2,241,321 Schlack May 6, 1941 FOREIGN PATENTS 61,475 Denmark Oct. ll,1943 906,181 France May 7, 1945

1. THE METHOD OF PREPARING A NEW POLYMERIC MATERIAL WHICH COMPRISESHEATING A CYCLIC CARBAMATE REPRESENTED BY THE GENERAL FORMULA